The present invention relates to a phase difference detection device and method for use in position detection and a position detection system which are applicable to detection of both rotational positions and linear positions, such as a rotational position detector like a resolver or synchro, or a linear position detector based on a similar position detecting principle. More particularly, the present invention relates to a technique to detect an absolute position on the basis of an electric phase difference.
Among various induction-type rotational position detectors, one which produces two-phase (sine phase and cosine phase) outputs in response to a single-phase exciting input is commonly known as a xe2x80x9cresolverxe2x80x9d, and others which produce a three-phase (phases shifted 120xc2x0 in relation to one another) outputs in response to a single-phase exciting input is known as a xe2x80x9csynchroxe2x80x9d. The oldest-fashioned resolvers have double-pole (sine pole and cosine pole) secondary windings provided on the stator in such a manner to cross each other at a mechanical angle of 90xc2x0, with a primary winding provided on the rotor (the relationship between the primary and secondary windings may be reversed depending on a desired application). However, the resolvers of this type are disadvantageous in that they require brushes for electric contact with the primary winding on the rotor. Brushless resolvers eliminating the need for such brushes are also known, where a rotary transformer is provided on the rotor in place of the brushes.
R/D converters have long been known as a detection system which obtains position detection data in digital form by use of a resolver which produces a two-phase (sine phase and cosine phase) outputs in response to a single-phase exciting input.
U.S. Pat. No. 3,648,042 discloses a technique which provides a rotation angle detection signal of a resolver as an analog voltage signal. Further, U.S. Pat. No. 4,011,440 discloses a technique which generates, on the basis of an output signal from a resolver, a cyclic square-wave signal having a pulse width corresponding to a detected angle and provides an angular rate on the basis of differences between pulse widths in individual cycles.
Another detection system is also known, where the resolver exciting method is modified to produce a single-phase output in response to two-phase exciting inputs so that an output signal containing an electric phase difference angle corresponding to rotational angle xcex8 is obtained to thereby derive digital data indicative of a detected angle xcex8. Specific examples of the above-mentioned phase difference detection system are disclosed in U.S. Pat. Nos. 4,754,220, 4,297,698, etc.
As known in the art, windings of a sensor such as the resolver tend to undesirably change in impedance under the influence of ambient temperature change, and thus electric phase of A.C. signals induced in a secondary winding subtly fluctuates in response to the temperature change. Additionally, the electric phase of the induced A.C. signals received by a detection circuit varies under the influence of various factors other than a position-to-be-detected, such as ununiform wiring lengths between the windings of the sensor and the detection circuit and delays in various circuit operations. If the phase variation based on the various factors, other than the position-to-be-detected, such as the temperature change is expressed by xe2x80x9cxc2x1dxe2x80x9d for convenience of description, in the former-type detection system, i.e., the R/D converter, the variation amount xe2x80x9cxc2x1dxe2x80x9d is in effect cancelled out and hence has no effect at all on the detecting accuracy. Therefore, it can be seen that the detection system like the R/D converter is a high-accuracy system insusceptible to adverse influence of the ambient temperature change. However, because this detection system is based on a so-called xe2x80x9csuccessive incrementing methodxe2x80x9d where, as noted earlier, a reset trigger signal is periodically applied to a sequential phase generation circuit at optional timing to reset a phase angle xcfx86 to xe2x80x9c0xe2x80x9d so as to initiate incrementing of the angle xcfx86, and the incrementing of the phase angle xcfx86 is stopped upon arrival at xe2x80x9c0xe2x80x9d of the output of a subtracter to thereby obtain digital data indicative of a detected angle xcex8, it has to wait for a period from the time when the reset trigger is given to the time when the phase angle xcfx86 coincides with the detected angle xcex8 and hence presents poor response characteristics.
On the other hand, in the latter-type detection system, the phase variation amount xe2x80x9cxc2x1dxe2x80x9d based on the non-positional factors (other than the position-to-be-detected) such as temperature change presents a very significant problem that the variation xe2x80x9cxc2x1dxe2x80x9d directly appears as a detection error.
The scheme of generating phase detection data in digital representation permits a high-accuracy detection, but is disadvantageous in that it would require an increased number of detection-signal transmitting lines if the digital detection data are transmitted directly in a parallel fashion.
It is therefore an object of the present invention to provide a phase difference detection device and method for use with a position detector which can perform a high-accuracy position detection without being influenced by unwanted phase variation caused by various factors, other than a position-to-be-detected, such as impedance change in a position sensor due to temperature change, which presents superior high-speed response characteristics, or which can significantly simplify detection-signal transmission lines and also minimize adverse influences of external disturbances, such as temperature changes, on the detection signal on the transmission lines.
In order to accomplish the above-mentioned object, the present invention provides a phase difference detection device for a position detector, said position detector being excited by a predetermined reference signal to generate first and second A.C. output signals, said first A C. output signal having been amplitude-modulated using, as an amplitude coefficient, a first function value corresponding to a position-to-be-detected, and said second A.C. output signal having been amplitude-modulated using, as an amplitude coefficient, a second function value corresponding to the position-to-be-detected, said phase difference detection device comprises: a phase shift circuit operatively coupled to said position detector to shift an electric phase of said received first A.C. output signal by a predetermined angle; a first circuit operatively coupled to said phase shift circuit and said position detector to perform an operation between an output signal of said phase shift circuit and said second A.C. output signal so as to synthesize a first data signal having an electric phase angle shifted in one of positive and negative directions in correspondence to the position-to-be-detected; a second circuit operatively coupled to said phase shift circuit and said position detector to perform an operation between an output signal of said phase shift circuit and said second A.C. output signal so as to synthesize a second data signal having an electric phase angle shifted in other of positive and negative directions in correspondence to the position-to-be-detected; a first operation circuit operatively coupled to said first circuit to measure an electric phase difference between said predetermined reference signal and said first data signal to obtain first phase data; a second operation circuit operatively coupled to said second circuit to measure an electric phase difference between said predetermined reference signal and said second data signal to obtain second phase data; a third operation circuit operatively coupled to said first and second operation circuit to calculate position detection data corresponding to the position-to-be-detected on the basis of said first and second phase data; and a pulse-width modulation circuit coupled to said third operation circuit to generate a signal pulse-width-modulated in accordance with the position detection data.
The position detector generates the first and second output signals (e.g., sinxcex8xc2x7sinxcfx89t and cosxcex8xc2x7sinxcfx89t) amplitude-modulated by two different function values in correspondence to the position-to-be-detected (x) is a known detector or sensor such as a resolver. The present invention is characterized in that output signals from such a known position detector (i.e., output signals to which phase-modulation corresponding to the position-to-be-detected has not been applied) is input to the device for detection of a phase difference thereof so that an absolute position can be detected on the basis of the phase difference detection, and the detected absolute position data is converted to a pulse-width-modulated signal for transmission.
Namely, by performing an addition and/or subtraction between the output signal (sinxcex8xc2x7cosxcfx89t) derived by shifting the electric phase of the first A.C. output signal received from the position detector by a predetermined angle and the second A.C. output signal (cosxcex8xc2x7sinxcfx89t), the first and second data signals (e.g., sin(xcfx89t+xcex8) and sin(xcfx89txe2x88x92xcex8)) are synthesized which have an electric phase angle corresponding to the position-to-be-detected. In a specific example, the first data signal (sin(xcfx89t+xcex8)) phase-shifted in a positive direction can be synthesized on the basis of the addition, e.g., (sinxcex8xc2x7cosxcfx89t+cosxcex8xc2x7sinxcfx89t), while the second data signal (sin(xcfx89txe2x88x92xcex8)) phase-shifted in a negative direction can be synthesized on the basis of the subtraction, e.g., (xe2x88x92sinxcex8xc2x7cosxcfx89t+cosxcex8xc2x7sinxcfx89t).
If a fundamental time-varying phase of the obtained A.C. signal is represented by xe2x80x9cxcfx89txe2x80x9d and phase variation caused by impedance change of the detector""s wiring due to temperature change and other factors than the position-to-be-detected (i.e., non-positional factors) is represented by xe2x80x9cxc2x1dxe2x80x9d, then the first data signal may be expressed as xe2x80x9csin(xcfx89txc2x1d+xcex8)xe2x80x9d and the second data signal as xe2x80x9csin(xcfx89txc2x1dxe2x88x92xcex8)xe2x80x9d. That is, the electrical phase differences (xcex8), corresponding to the position-to-be-detected (x), for the first and second data signals appear as opposite (positive and negative)-direction phase shifts. However, the phase variations xe2x80x9cxc2x1dxe2x80x9d for both of the first and second data signals have effects in the same positive or negative direction depending on the current conditions. Thus, by measuring the respective phase differences xe2x80x9c(xc2x1d+xcex8)xe2x80x9d and xe2x80x9c(xc2x1dxe2x88x92xcex8)xe2x80x9d of the first and second data signals and performing an appropriate operation such as an addition and/or subtraction on the measured differences, it is allowed to cancel out or extract the phase variation xe2x80x9cxc2x1dxe2x80x9d and also detect the phase difference (xcex8) free of the phase variation xe2x80x9cxc2x1dxe2x80x9d which accurately corresponds to the position-to-be-detected (x).
The detected phase difference (xcex8), i.e., position detection data, is pulse-with-modulated via a pulse-width modulation circuit, to provide a pulse-width-modulated position detection signal having a pulse with corresponding to the phase difference (xcex8). The pulse-width-modulated position detection signal is then supplied via transmission wirings or lines to another device utilizing the signal (hereinafter called a xe2x80x9cutilizing devicexe2x80x9d). Transmission of the detected position data in the form of the pulse-width-modulated position detection signal is advantageous in that it can simplify the transmission wirings or lines and prevent voltage level variations of the signal, due to various adverse influences on the signal passing through the wirings such as impedance variations by the influence of wiring capacity, noise and temperature changes, from causing errors to the position detection signal, thereby constantly guaranteeing a high detection accuracy.
Consequently, the present invention permits a high-accuracy position detection without being influenced by various factors, other than the position-to-be-detected, such as impedance change of the sensor due to temperature change and ununiform lengths of wiring cables. Further, because the present invention is based on the technique of measuring a phase difference (xcex8) in A.C. signals, the instant latching method may be employed rather than the conventional successive incrementing method, and thus the invention can achieve a phase difference detection device or method which presents superior high-speed characteristics. In addition, by transmitting the detected position data in the form of the pulse-width-modulated position detection signal as mentioned above, there is achieved the superior benefit that the transmission wirings or lines can be significantly simplified and various adverse influences on the signal passing through the wirings can be reliably avoided.
In one implementation, the third operation circuit may calculate the position detection data as analog position detection data, and the pulse-width modulation circuit may include an analog circuit for processing the analog position detection data.
Alternatively, the third operation circuit may calculate the position detection data as digital position detection data, and the pulse-width modulation circuit may include a digital circuit for processing the digital position detection data.
In another alternative, the third operation circuit may calculate the position detection data as digital position detection data, and the phase difference detection device further may include a converter for converting the digital position detection data into analog position detection data. In this case, the pulse-width modulation circuit may include an analog circuit for processing the analog position detection data.
According to another aspect of the present invention, there is provided a phase difference detection device for a position detector, the position detector being excited by a predetermined reference signal to generate first and second A.C. output signals, the first A C. output signal having been amplitude-modulated using, as an amplitude coefficient, a first function value corresponding to a position-to-be-detected, and the second A.C. output signal having been amplitude-modulated using, as an amplitude coefficient, a second function value corresponding to the position-to-be-detected, which is characterized by comprising: a phase shift circuit operatively coupled to the position detector to shift an electric phase of the received first A.C. output signal by a predetermined angle; a first circuit operatively coupled to the phase shift circuit and the position detector to perform an operation between an output signal of the phase shift circuit and the second A.C. output signal so as to synthesize a first data signal having an electric phase angle shifted in one of positive and negative directions in correspondence to the position-to-be-detected; a second circuit operatively coupled to the phase shift circuit and the position detector to perform an operation between an output signal of the phase shift circuit and the second A.C. output signal so as to synthesize a second data signal having an electric phase angle shifted in other of positive and negative directions in correspondence to the position-to-be-detected; and a third circuit operatively coupled to the first and second circuit to generate, on the basis of a difference between the first data signal and the second data signal, a signal pulse-modulated in accordance with position data indicative of the position-to-be-detected.
The present invention may be constructed and implemented not only as the above-mentioned device invention but also as a method invention. The method may be arranged and implemented as a program for execution by a computer, microprocessor or the like, as well as a machine-readable storage medium storing such a program.